Information Management (Chapter 3)

Key

One or more attributes that determine other attributes.

Primary key (PK)

An identifier composed of one or more attributes that uniquely identifies an entity.

Composite key

A multiple-attribute key.

Key attribute

An attribute that is part of a primary key

Superkey

An attribute or attributes that uniquely identify each attribute. It is not yet a primary key.

Candidate key

A minimal superkey; that is, a key that does not contain a subset of attributes that is itself a superkey.

Entity integrity

It guarantees each entity has a unique value in a primary key and that the key has no null values.

Null

The absence of an attribute value. Note that a null is not a blank

Foreign key (FK)

An attribute or attributes in one table/entity whose values must match the primary key in another table/entity or whose values must be null.

Referential integrity

A condition by which a dependent table’s/entity’s foreign key must have either a null entry or a matching entry in the related table/entity.

Domain

The possible set of values for a given attribute

Required attribute

In ER modeling, an attribute that must have a value. In other words, it cannot be left empty.

Optional attribute

In ER modeling, an attribute that does not require a value; therefore, it can be left empty.

Identifier

One or more attributes that uniquely identify each entity instance.

Relational schema

The organization of a relational database as described by the database administrator

Composite identifier

In ER modeling, a key composed of more than one attribute.

Composite attribute

An attribute that can be further subdivided to yield additional attributes

Simple attribute

An attribute that cannot be subdivided into meaningful components

Single-valued attribute

An attribute that can have only one value.

Multivalued attribute

An attribute that can have many values for a single entity occurrence.

Derived attribute

An attribute that does not physically exist within the entity and is derived via an algorithm. Sometimes referred to as computed attributes

Participants

An ER term for entities that participate in a relationship.

Connectivity

The classification of the relationship between entities. Classifications include 1:1, 1:M, and M:N.

Cardinality

A property that assigns a specific value to connectivity and expresses the range of allowed entity occurrences associated with a single occurrence of the related entity.

Existence-dependent

A property of an entity whose existence depends on one or more other entities.

Existence-independent

A property of an entity that can exist apart from one or more related entities.

Strong entity

An entity that is existence-independent, that is, it can exist apart from all of its related entities, Also called Regular Entity

Weak (nonidentifying) relationship

A relationship in which the primary key of the related entity does not contain a primary key component of the parent entity.

Strong (identifying) relationship

A relationship that occurs when two entities are existencedependent; from a database design perspective, this relationship exists whenever the primary key of the related entity contains the primary key of the parent entity.

Weak entity

An entity that displays existence dependence and inherits the primary key of its parent entity

Optional participation

In ER modeling, a condition in which one entity occurrence does not require a corresponding entity occurrence in a particular relationship.

Mandatory participation

A relationship in which one entity occurrence must have a corresponding occurrence in another entity.

Relationship degree

The number of entities or participants associated with a relationship. A relationship degree can be unary, binary, ternary, or higher.

Unary relationship

An ER term used to describe an association within an entity. It is known as a recursive relationship

Binary relationship

An ER term for an association (relationship) between two entities

Ternary relationship

An ER term used to describe an association (relationship) between three entities.